The present invention is a biodegradable (synonymously bioresorbable), biocompatible, pliable, knitted silk matrix, mesh or scaffold (the “device”) and methods for making and using the device in surgical and cosmetic procedures where soft tissue (i.e. a gland, organ, muscle, skin, ligament, tendon, cartilage, blood vessel or mesentery) support (through the load bearing function of the device) is desired, such as for example in breast reconstruction, breast augmentation, abdominal surgery, gastro-intestinal surgery, hernia repair and facial surgery. The soft tissue support can be provided by the device itself (for example in conjunction with a hernia repair) or by the device being used in conjunction with another implant, for example use of the device on or around a tissue expander or a breast implant used in a breast reconstruction or a breast augmentation surgical procedure.
Soft tissue support surgical meshes and scaffolds are known and are usually made of a synthetic polymer such as Teflon®, polypropylene, polyglycolic acid, polyester, or polyglactin 910. Biomaterials such a tissue based or tissue derived material, for example an acellular dermal matrix (“ADM”) obtained from human and animal derived dermis have also been used but do not have the mechanical integrity of high load demand applications (e.g. ligaments, tendons, muscle) or the appropriate biological functionality because most biomaterials either degrade too rapidly (e.g., collagen, PLA, PGA, or related copolymers) or are non-degradable (e.g., polyesters, metal), and in either case functional autologous tissue ingrowth (important to assist transfer of a load bearing function from an implanted biomaterial as the biomaterial is bioresorbed by the body) occurs very little or fails to occur. In certain instances a biomaterial may misdirect tissue differentiation and development (e.g. spontaneous bone formation, tumors) because it lacks biocompatibility with surrounding cells and tissue. As well, a biomaterial that fails to degrade typically is associated with chronic inflammation and such a response is detrimental to (i.e. weakens) surrounding and adjacent tissue.
Silk is a natural (non-synthetic) protein made of high strength fibroin fibers with mechanical properties similar to or better than many of synthetic high performance fibers. Silk is also stable at physiological temperatures in a wide range of pH, and is insoluble in most aqueous and organic solvents. As a protein, unlike the case with most if not all synthetic polymers, the degradation products (e.g. peptides, amino acids) of silk are biocompatible. Silk is non-mammalian derived and carries far less bioburden than other comparable natural biomaterials (e.g. bovine or porcine derived collagen). Silk, as the term is generally known in the art, means a filamentous fiber product secreted by an organism such as a silkworm or spider. Silks can be made by certain insects such as for example Bombyx mori silkworms, and Nephilia clavipes spiders. There are many variants of natural silk. Fibroin is produced and secreted by a silkworm's two silk glands. As fibroin leaves the glands it is coated with sericin a glue-like substance. Spider silk s produced as a single filament lacking the immunogenic protein sericin. Use of both silkworm silk and spider silk (from a natural source or made recombinantly) is within the scope of the present invention.
Silkworm silk has been used in biomedical applications. The Bombyx mori species of silkworm produces a silk fiber (a “bave”) and uses the fiber to build its cocoon. The bave as produced include two fibroin filaments or broins which are surrounded with a coating of the gummy, antigenic protein sericin. Silk fibers harvested for making textiles, sutures and clothing are not sericin extracted or are sericin depleted or only to a minor extent and typically the silk remains at least 10% to 26% by weight sericin. Retaining the sericin coating protects the frail fibroin filaments from fraying during textile manufacture. Hence textile grade silk is generally made of sericin coated silk fibroin fibers. Medical grade silkworm silk is used as either as virgin silk suture, where the sericin has not been removed, or as a silk suture from which the sericin has been removed and replaced with a wax or silicone coating to provide a barrier between the silk fibroin and the body tissue and cells. Physicians prefer and require an implantable, knitted silk medical device with the flexibility to be stretched, expanded, pulled into shape, elongated and/or draped into place over, around or under soft tissue or an implant at the time of a soft tissue surgical or medical procedure, without the silk medical device upon its elongation breaking, splitting or unraveling. Thus there is a need for such a pliable, sericin extracted implantable, bioresorbable silk medical device.